Why do my legs and feet turn red?

Whenever I stand for a while my feet, legs, and sometimes knees, will turn bright red or slightly purple and be really warm to the touch. They also sometimes swell or itch. If I have been sitting for a long time they might turn a bluish purple or bright red again. It was never this bad until I had hamstring/ hip surgery when I was 14. We figured it would go away after a while because we thought the surgery probably caused. It has only gotten worse over the years. I am 17 now and I just had acl replacement surgery and it has been getting even worse. Does anyone know what this is or how to help it? PLEASE HELP. It's no fun walking around looking like I have sunburn all the time. :P